Coupling between laser modes has been considered by many investigators in the prior art, see for example, W. E. Lamb, Physics Review, 134A 1429 (1964); J. A. Texter and E. E. Bergmann, Physics Review, A Volume 9, No. 6 P2649, June 1974. Coupled lasers have been studied extensively, see for example, M. B. Spencer and W. E. Lamb, Physics Review A, Volume 5, No. 2 P893, February 1972; and the injection locking effect has been used to make efficient and fast modulators, see for example, L. G. DeShayer and E. A. Maunders, I.E.E.E. Journal of Quantum Electronics, Volume QE4, No. 10, P642, October 1968.
The techniques described in the aforesaid publications, however, require precise spectral and cavity control. Another type of optical modulator is also known to the prior art, which is based on variations of the transmission characteristics of a Fabry-Perot cavity which occur when the cavity is filled with a saturable absorber, see for example Seidel U.S. Pat. No. 3,610,731 and S. L. McCall Physics Review 4, Volume 9, P1515, 1974; or with a medium with a non-linear index of refractions, see T. Griechkowsky, Applied Physics Letters, Volume 31, No. 7, P437, October 1977.
The opto-optic modulator of the present invention represents a distinct improvement over the modulators described in the aforesaid publications in that it is eminently simple in its construction and control, and economical and inexpensive to construct. The opto-optic modulator of the invention has wide utility in the field of optical signal generation and processing. The modulator, as described briefly above, uses one light signal to modulate another with gain.
The modulator of the invention is basically an inverter, in that an increase in the intensity of the control optical signal causes a decrease in the intensity of the controlled optical signal. Thus, the implementation of optical equivalents to many electrical and electronic circuits in the practice of the invention is possible. For example, optical equivalents of differential amplifiers, comparators, delay oscillators, and the like, are possible in accordance with the invention.
The basic operating principle of the opto-optic modulator of the invention is premised upon the cross-saturation of two light beams in a gain medium. As pointed out above, if the gains of the two beams in the medium are different, variations of one beam will have a greater effect on the other, resulting in an efficient modulator with gain. Two embodiments of the opto-optic modulator of the invention will be described herein, namely, a modulated amplifier and a modulated oscillator.
As noted above, the advantages of the saturation-based modulators of the present invention include simple fabrication. In addition, the opto-optic modulators exhibits low level input intensity requirements, and applications to both large scale and integrated optical laser systems are feasible. Moreover, substantial amounts of gain are readily available in the opto-optic modulator.